Vanilla is a flavouring material derived from the pods of the vanilla orchid. It has long been known to make vanilla extract by extracting vanilla pods with alcohol (ethanol). More recently, vanilla pods have been extracted with supercritical carbon dioxide, generally in conjunction with a co-solvent such as ethanol. Flavourant components dissolve in the carbon dioxide (and co-solvent), which is then separated from the solid (waste) material.
Because of the expense of vanilla pods, there have long been attempts to produce substitutes. The main constituent of vanilla flavour is vanillin (3-methoxy-4-hydroxybenzaldehyde). This has been produced from industrial waste materials such as sulphite waste liquors of the wood pulp industry. However it is not possible to make “natural grade” vanillin in this way, and such material is unacceptable to many.
It must be appreciated that the natural vanilla aroma and flavour originating in vanilla pods are due to a complex mixture of compounds, mostly phenolic, of which vanillin is merely the main one in terms of percentage composition. It generally constitutes something less than 3% by weight of vanilla pods. Someone seeking to produce “vanilla extract” from vanilla pods is not seeking to extract vanillin selectively, but to extract a mixture (which may be concentrated to produce a brownish oil). In contrast someone seeking pure vanillin would not consider vanilla pods as a starting material—they are far too expensive, with a low vanillin content—and the technology developed for preparing vanilla extracts would not be considered relevant.
It is known to convert ferulic acid into vanillin using various microorganisms. We have previously disclosed (WO 00/50622) that use of a special strain of Pseudomonas putida can lead to a culture medium containing 2.25 gl−1 of vanillin, a molar yield of 75% based on ferulic acid consumed. Vanillin was recovered by separating the culture broth from the cells and extracting it with an organic solvent (butyl acetate).
Haarman & Reimer GmbH have disclosed (U.S. Pat. No. 6,133,003) two strains of Amycolatopsis. Using one of them they achieved a culture medium containing up to 11.5 gl−1 of vanillin and 1 gl−1 of unreacted ferulic acid. These concentrations were determined by HPLC. There is no disclosure of any work-up technique or the isolation of the product.
Givaudan-Roure (International) S.A. have disclosed (EP-A-0885968) the use of Streptomyces setonii to produce “vanillin and several by-products”. The concentration of vanillin is said to be 8-16 gl−1, though in the actual examples it ranges from 3.10 to 13.9 gl−1, in the latter case accompanied by 0.4 gl−1 of guaiacol. The co-production of guaiacol is represented as being advantageous. The products are extracted by solvent extraction using methyl tert-butyl ether.
In many fields, the use of organic solvents is now seen as undesirable. This is certainly the case in the production of food-grade materials, especially if they are to be of “organic” quality.